* reorder ssz
* split into hash_trees and ssz_serialization, roughly, for hashing and
IO
* move bitseqs into ssz (from stew)
* clean up imports
* docs, imports
- we have a new binary which connects via RPC to the respective BN and has an internal clock - waking it up on every slot
- the BN has a new option called --external-validators and currently in order to have the VC binaries to run we need to pass EXTERNAL_VALIDATORS=yes to make
- factored some code out of beacon_node.nim for easier reuse in validator_api.nim and validator_client.nim
- the VC loads its associated private keys from the datadir for its BN
- most of the validator API calls have been implemented as a stub.
- the VC polls its BN at the start of each epoch - getting a list of all active validators for the current epoch - and then continues to request blocks and sign them with its appropriate validators when necessary
* in makeBeaconBlock - use rollback instead
* in tests - this helps state_sim give more accurate data and makes it
30% faster
* fix some usages of raw BeaconState
* fix some warnings related to beacon_node splitting; reimplement finalization verification more robustly; improve attestation pool block selection logic
* re-add missing import
* whitelist allowed state transition flags and make rollback/restore naming more consistent
* restore usage of update flags passed into skipAndUpdateState(...) in addition to the potential verifyFinalization flag
* switch rest of rollback -> restore
Mamy Ratsimbazafy
Jacek Sieka
Dustin Brody
Viktor Kirilov
Zahary Karadjov